The present invention relates to a process for producing a hydrophilic polyolefin nonwoven fabric which comprises treating with a plasma a nonwoven fabric of fibers of a polyolefin containing a hindered amine compound.
Nonwoven fabrics of polyolefin fibers have found use in a broad range of applications as battery separator, filter, packaging material, construction material, sanitary napkin, and so on. Being hydrophobic, polyolefin nonwoven fabrics are required to be made hydrophilic when they are used as, for example, battery separators which should have a hydrophilic nature. To impart the hydrophilic nature, the nonwoven fabric is impregnated with a surface active agent in the final stage of production, or the nonwoven fabric is sprayed with an aqueous solution of surface active agent immediately after the fibers have been extruded from the nozzle in the intermediate stage of production. The nonwoven fabrics made hydrophilic in this way have a disadvantage in that the surface active agent is lost during use for a long period of time and the hydrophilic nature becomes poor.
In order to keep the hydrophilic nature, there was proposed a process for treating a polyolefin nonwoven fabric with a plasma (Japanese Patent Laid-open No. 94752/1983). The plasma treated polyolefin nonwoven fabric maintains its hydrophilic nature over a long period of time; however, the plasma treatment takes a long time and is poor in productivity. On the other hand, there is disclosed in Japanese Patent Laid-open No. 179240/1983 a process for improving the bondability of polyolefin moldings containing a hindered amine by means of plasma treatment. This process, however, does not improve the hydrophilic nature of nonwoven fabrics composed of fine fibers of polyolefin.